The present invention generally relates to surgical instruments and more particularly relates to a tissue cutting surgical device suitable for use in vitreous and retinal surgery.
An eye surgery procedure performed behind the lens is called vitreous surgery in as much as the posterior chamber of the eye is filled with a transparent jelly called the vitreous humor (xe2x80x9cvitreousxe2x80x9d).
Understandably, vitreous surgery, as with any ophthalmic surgical procedure, requires great precision. The vitreous is filled with numerous fiber like materials, some of which are attached to the delicate retina. The presence of these fibers make vitreous surgery quite difficult, due to the possibility of retinal injury occurring if one of these fibers is inadvertently severed.
Moreover, retinal surgery, which involves actual cutting of the retina of the eye, must be performed with even greater precision, as the retina is the immediate instrument of vision and is directly connected with the brain by the optic nerve. Thus, a surgical instrument suitable for use in vitreous surgery may not be suitable for use in retinal surgery.
For example, the state of the art vitreous cutter comprises a hand held probe having a cutting tip thereon.
The cutting tip comprises an outer tube having a perforation therein, and an inner tube having a reciprocating cutting edge for shearing portions of tissue drawn into the outer tube perforation. The inner tube is typically driven in an axially reciprocating fashion, at a cutting rate of about 400 strokes per minute, by pneumatic means. More particularly, the pneumatic means typically includes a pressurized air source which supplies periodic bursts of air that drive the inner tube forward within the outer tube. A diaphragm or spring is included in the probe which biases the inner cutting tube backward to a home position. Thus, the cutting strokes of the inner tube are controlled by periodic bursts of air forcing the inner cutting tube forward, alternating with the discontinuing thereof such that the biased spring forces the cutting tube backward.
It well known that such pneumatically driven devices do not operate effectively at very low speeds and are designed for operation at high speeds, for example, hundreds of cycles per minute. Moreover, although the cutting rate provided by such instruments may be controllable to some extent, control over speed and length of an individual cutting stroke is not obtainable. Thus, such cutters may be inappropriate for use in retinal surgery, which requires exceptional precision and control in order to avoid serious injury to the patient.
The present invention provides a ophthalmic surgical cutting instrument that can be operated at very low speeds in order to provide to superior control of cuts made thereby. The instrument in accordance with the present invention may also be operated quite effectively at high speeds when the nature of the surgery so requires.
Accordingly, a surgical cutting device in accordance with the present invention generally comprises a probe having a cutting tip comprised of an outer sleeve and an inner cutter sleeve. This type of cutting tip, as will now be generally described, is presently well known in the art. More specifically, the outer sleeve includes a perforation proximate a distal end of the outer sleeve which provides means for receiving a portion of tissue to be incised. The cutter sleeve is slidably and coaxially disposed in the outer sleeve and includes a cutting edge at a distal end thereof. When the probe tip is urged against a portion of tissue, such as a portion of the vitreous humor, the portion will protrude through the perforation in the outer sleeve and be sheared by a axially reciprocating motion of the cutter sleeve.
Importantly, the present invention also comprises mechanical means for driving the stroking motion of the cutter sleeve at a selected stroke rate of down to about one stroke per minute, or in other words, at an exceptionally slow speed. The mechanical means, which will be described in greater detail hereinafter, enable a physician to control amount and speed of individual strokes of the stroking motion. Moreover, the present invention enables a physician to achieve even a fraction of a cut, if so desired.
More particularly, the mechanical means includes a coaxial cable as means for connecting the probe to a motor adapted for moving the cutter sleeve in an incremental or stroking motion, for example a stepper motor. The cable may comprise an outer stationary cable and an inner cable slidably disposed therein and mounted in operative relationship with the cutter sleeve. A spring may be included within the probe for biasing the cutter sleeve in a home position. Thus, the inner cable and reciprocating cutter sleeve are moved back and forth by alternating forces exerted by the stepper motor and the spring.
An aspiration line, in fluid communication with a bore in the cutter sleeve, may also be provided. More particularly, the aspiration line may be connected to a vacuum source, and may provide means for both gently drawing the portion of tissue into the outer tube perforation and subsequently removing the portion of tissue from the probe to a collection vessel after the cutter sleeve has severed said portion as described hereinabove.
By selection of an appropriate stepper motor, the cutter sleeve may be driven at a selected stroking rate of between about one and about one thousand or more cuts per minute.